The invention relates to the field of hydrodynamic bearing assemblies of the type that cooperates with high-speed spindle elements. More specifically, the invention relates to setting gaps in hydrodynamic bearing assemblies utilized in a disc drive system.
Disc drive memory systems have been used in computers for many years for storage of digital information. Information is recorded on concentric memory tracks of a magnetic disc medium, the actual information being stored in the form of magnetic transitions within the medium. The discs themselves are rotatably mounted on a spindle. The information is accessed by means of read/write heads generally located on a pivoting arm that moves radially over the surface of the disc. The read/write heads or transducers must be accurately aligned with the storage tracks on the disc to ensure proper reading and writing of information.
During operation, the discs are rotated at very high speeds within an enclosed housing by means of an electric motor generally located inside a hub that supports the discs. One type of motor in common use is known as an in-hub or in-spindle motor. Such in-spindle motors typically have a spindle mounted by means of two ball or hydrodynamic bearing systems to a motor shaft disposed in the center of the hub. Generally, such motors include a stator comprising a plurality of teeth arranged in a circle. Each of the teeth support a plurality of coils or windings that may be sequentially energized to polarize the stator. A plurality of permanent magnets are disposed in alternating polarity adjacent the stators. As the coils disposed on the stators are sequentially energized in alternating polarity, the magnetic attraction and repulsion of each stator to the adjacent magnets cause the spindle to rotate, thereby rotating the disc and passing the information storage tracks beneath the head.
The use of hydrodynamic bearing assemblies in such drive systems has become preferred due to desirable reductions in drive size and noise generation as compared to conventional ball bearing drive systems. In hydrodynamic bearings, a lubricating fluid, such as oil or air, functions as the bearing surface between a stationary base or housing and a rotating spindle or hub. As the lubricating fluids require small gaps between the stationary and rotating members in order to provide the support, stiffness and lubricity required for proper bearing operation, conventional drive components and assemblies typically require tight tolerances and demand precision assembly methods. Such demanding tolerance and assembly control results in increased part and assembly costs along with an increased level of quality control to ensure proper drive operation.
Thus, the problem presented is to reliably set close bearing gaps without requiring excessive or burdensome part or manufacturing tolerances.
A method for setting one or more hydrodynamic bearing gaps in a disc drive spindle motor is provided. In one embodiment, a method for setting one or more hydrodynamic bearing gaps in a disc drive spindle motor includes disposing a rotary member against one or more working surfaces such that substantially no gap exists therebetween and inducing creep between the rotary member and the working surfaces. The creep creates a bearing gap therebetween the rotary member and at least one of working surfaces. The creep may be induced by thermally cycling the motor components or applying a force to a tool coupled to a member having at least one of the working surfaces disposed thereon.
The invention is useful in disc drive spindle motors having hydrodynamic bearings to set bearing gaps without tight assembly tolerances which would necessitate burdensome quality control procedures to confirm proper gap set and motor operation. Additionally, the invention allows the relaxation of tight component tolerances demanded in conventional designs resulting in lower component cost and reject rates.